Short description: Unified quantum field theory describing the electromagnetic and weak interactions via SU(2) × U(1) gauge symmetry

Electroweak theory is the unified quantum field theory that combines the electromagnetic and weak interactions into a single framework based on the gauge symmetry group $S U (2)_{L} \times U (1)_{Y}$ .^[1] It forms a central part of the Standard Model of particle physics.

Electroweak unification: electromagnetic and weak interactions arising from a single gauge structure

Unification of forces

Electroweak theory shows that the electromagnetic force and weak nuclear force are different manifestations of a single interaction at high energies.

At low energies:

electromagnetic interaction → long-range force
weak interaction → short-range force

At high energies, they merge into a unified electroweak interaction.^[2]

Gauge symmetry

The theory is based on the symmetry group: $S U (2)_{L} \times U (1)_{Y}$

where:

$S U (2)_{L}$ acts on left-handed fermions
$U (1)_{Y}$ corresponds to weak hypercharge

Gauge fields are introduced to preserve local symmetry, leading to four gauge bosons.^[3]

Gauge bosons

The electroweak theory predicts four gauge bosons:

$W_{μ}^{1}, W_{μ}^{2}, W_{μ}^{3}$ (from $S U (2)$ )
$B_{μ}$ (from $U (1)$ )

These combine to form the physical particles:

$W^{+}$ and $W^{-}$ (charged weak bosons)
$Z^{0}$ (neutral weak boson)
$γ$ (photon)

This mixing explains how electromagnetic and weak forces are related.^[1]

Spontaneous symmetry breaking

The electroweak symmetry is not directly observed because it is spontaneously broken.

This occurs through the Higgs mechanism, introducing a scalar field whose vacuum expectation value selects a specific ground state: $⟨ ϕ ⟩ \neq 0$

As a result:

$W^{\pm}$ and $Z^{0}$ acquire mass
the photon remains massless

This explains the short range of the weak interaction.^[4]

Electroweak Lagrangian

The electroweak Lagrangian includes:

fermion kinetic terms
gauge field terms
Higgs field contributions
interaction terms

These components together describe the full dynamics of the electroweak interaction.

Weak interactions

The weak interaction involves processes such as:

beta decay
neutrino interactions
flavor-changing processes

These are mediated by the $W^{\pm}$ and $Z^{0}$ bosons.

Experimental confirmation

Electroweak theory has been confirmed by numerous experiments, including:

discovery of the $W$ and $Z$ bosons
precision measurements at particle accelerators
observation of the Higgs boson

These results strongly support the validity of the theory.^[3]

Role in the Standard Model

Electroweak theory, together with quantum chromodynamics, forms the core of the Standard Model.

It unifies two of the fundamental forces and provides a consistent framework for describing particle interactions.

Conceptual importance

Electroweak theory demonstrates how gauge symmetry and spontaneous symmetry breaking combine to produce realistic physical theories.

It is a cornerstone of modern particle physics and a key step toward deeper unification.

Table of contents (137 articles)

Index

Core theory

Foundations
Conceptual and interpretations
Mathematical structure and systems
Atomic and spectroscopy
Wavefunctions and modes
Quantum dynamics and evolution
Measurement and information
Quantum information and computing

Applications and extensions

Quantum optics and experiments
Open quantum systems
Quantum field theory
Statistical mechanics and kinetic theory
Condensed matter and solid-state physics
Plasma and fusion physics
Timeline
Advanced and frontier topics

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Physics:Quantum Electroweak theory

Unification of forces

Gauge symmetry

Gauge bosons

Spontaneous symmetry breaking

Electroweak Lagrangian

Weak interactions

Experimental confirmation

Role in the Standard Model

Conceptual importance

See also

Table of contents (137 articles)

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